A novel method is developed to determine the tensile strength of brittle fibers by means of a single-fiber fragmentation test. The parameters of Weibull distribution obtained from the fragmentation test can vary along with the variation of test condition because the difference of the test condition make the variation of stress recovery length where no fiber breaks can occur. The fragmentation tests with models of carbon fiber-reinforced vinylester and epoxy matrix composites are performed under some loading rates. Fragmentation test under Laser Raman Spectroscopy (LRS) is employed to measure the stress recovery length, and the parameters of Weibull distribution are derived from an analysis considering an effect of the stress recovery length. It is confirmed that the present method provides the constant fiber strength without reference to the difference of matrix and loading rate.

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The effects of fiber/matrix interfacial properties on the strength of unidirectional SiC/epoxy and SiC/bismaleimide composites were discussed experimentally. The interfacial properties are evaluated using microbond tests. Tensile tests on the unidirectional composites were also performed to clarify the relation between the interfacial properties and the composite strength. In the interfacial strength range of the present study, tensile strength were not influenced by the interfacial strength.

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Bulk Molding Compound is a popular engineering FRP and is used in Automobile and Electric instrument. Durability of BMC for machinery material was researched but today the application of this material has been developed in more hard circumstance. In the situation, this material was sometimes exposed by some cyclic loading-speeds and hard circumstances such as water absorption and high temperature. In this report, the effect of water absorption and frequency on bending strength and bending fatigue strength has been researched considering the distribution of mechanical properties. The fatigue fracture mechanisms were studied by observation method. From these result, it was found that crack initiation and propagation was mainly depended on delamination around glass fiber bundle.

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This study focused on a multi-axial knitted fabric which is expected as thick and high performance reinforcement for large scale composite structures. The effects of impact damage on multi-axial knitted CFRP laminates molded by vacuum assisted resin transfer molding (VARTM) method were evaluated. The impact damage inside material was evaluated by an ultrasonic scanning device and optical cross-sectional observation. Probed images obtained by both non-destructive and destructive methods were compared each other, and internal damage distribution of multi-axial knitted CFRP laminates was clarified. In addition, residual compressive strength and fatigue property of impact damaged CFRP laminates were evaluated. From the ultrasonic C-scan images and cross-sectional photographs, three-dimensional damage distribution of impacted CFRP laminate was obtained. Also by post impact fatigue (PIF) test, damage progress behavior was observed.

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The concept of ‘Damage Unit’ was employed to describe the fatigue damage of plain-woven carbon/epoxy composites and its progression. How the cluster formation of damage units and the distribution of damage units affected the fatigue damage progression behavior was studied. The thermoelastic damage analysis (TDA), which is one of non-destructive testing techniques for damage evaluation, was conducted to evaluate the fatigue damage state in the specimen during fatigue testing. Internal damage state was also observed on the polished edge-wise surface with a SEM. The experimental results showed that the size ratio of the maximum damage unit cluster C_max rapidly increased after the damage unit ratio p exceeded 0.527, called as “percolation threshold”,p_c. The final failure occurred because local delamination , fiber breakage and accumulation of transverse cracks widely occurred in the specimen after p exceeded p_c. Since the relationship between averaged thermoelastic damage response and C_max was nearly linear, fatigue damage progressed due to formation of damage unit cluster. The fractal dimensions of the damage unit distribution D increased to be a steady state value after p exceeded p_c. These results indicated that fatigue damage progression was accelerated when D increased beyond a steady state value.

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When an impact loading is applied to a sandwich panel with CFRP facesheets, the facesheet is bent in the out-of-plane direction and this deformation leads to deteriorations in the bending stiffness and the in-plane compressive strength. However, since the bending is elastic deformation, the facesheet will return to flat if the core buckling is repaired. Hence the authors developed shape memory alloy (SMA) honeycomb core and bonded the core to two CFRP facesheets, in which thin nichrome wires were embedded to heat the SMA core. When a voltage was applied to the nichrome wires, the core buckling caused by an impact loading disappeared and the deflection of the facesheet was relieved. This result shows that the SMA honeycomb core is effective for the suppression of the impact damage progress. Furthermore, the area repaired by the energization of the nichrome wire could be well simulated using a finite element analysis.

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Phase-shifting image plane digital holography is applied to displacement measurement of a cantilever beam. A sin/cos average fiter is used to reduce the noise in a phase difference image and the phase unwrapping technique proposed by Herráezet al. is used. The experimental results show that the above techniques are useful for phase unwrapping of phase difference images with noise. Also, strain calculation method used in finite element method are adopted to evaluate displacement gradient from experimental displacement data.The results show that the method can evaluate displacement gradient with high accuracy.

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Dynamic crack propagation in PMMA was studied using the method of caustics in combination with a Cranz-Schardin type high-speed camera. Four different types of specimen geometries were employed to achieve the crack acceleration, deceleration and/or re-acceleration process in one fracture event. Dynamic stress intensity factor K_ID and crack velocity á were evaluated in the course of crack propagation to obtain the relationships between K_ID and á . The effect of crack acceleration and deceleration on the K_ID-á relations was examined.

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Thermomechanical investigations of TiNi Shape Memory Alloy subjected to tension test were performed. Taking advantages from a thermovision camera, a temperature distribution on the specimen surface and the average temperature variation were found. Nucleation and development of the new martensitic and parent phases in the shape memory alloy subjected to stress-induced phase transformations were studied. It was observed during tension test that narrow inclined bands, similar to Lüders phenomena, of considerably higher temperature related to martensite phase appeared starting from the central part of the specimen and developing in two almost perpendicular directions towards grips. The non-uniform temperature distribution, related to the heterogeneous phase transformation, was observed also during unloading, while similar bands of the reverse transformation occur, accompanied by a significant temperature decrease. The bands of both martensite and parent phase fronts were characterized by the temperature variations of about 8 K and the slope of inclination of about 48 degrees.

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